Published CDC Services
Introduction
A Published CDC Service document defines which entities the Mendix Runtime tracks for object changes and publishes as Kafka events. Each tracked entity produces a stream of create, update, and delete events on its own Kafka topic.
Creating a Published CDC Service
To create a published CDC service, right-click a module in the App Explorer and choose Add other > Change data capture service. Studio Pro adds the document to that module for logical grouping, but the service operates at app level.
You can have multiple CDC service documents in an app, for example, to group entities by domain area or team ownership.
General
Service Name
The service name identifies the CDC service within the app. The app name is included in the topic name to ensure uniqueness across apps.
Description
This is an optional description for the CDC service.
Entities to Track
The Entities to track table lists the entities whose object changes are published to Kafka.
Use the toolbar to manage tracked entities:
- Add – add an entity from the domain model
- Remove – stop tracking a selected entity
- Accept changes – lock in the current Revision numbers after reviewing modifications
Entities
The Entities column refers to the domain model entity being tracked. Expand the row to view and select individual attributes and associations.
Exposed Name
The Exposed name column is the name used for this entity in the Kafka topic and event payload. It defaults to the entity name.
Modification
The Modification column refers to the pending change state: Added, Changed, or Removed. This will remain blank if the entity is unchanged since the last accepted revision.
Revision
The Revision column is the schema revision of the entity's event payload. See the Revisions section below for more information.
Topic
The Topic column is the Kafka topic name for this entity, in the format cdc.<app-name>.<ExposedName>.<revision>.{space}, where {space} is replaced at runtime by the Event Broker space name. See the Bring Your Own Kafka (BYOK) section of Change Data Capture for more information.
Attribute and Association Selection
Expand an entity row to see each attribute and association with a checkbox. Uncheck an item to exclude it from the event payload. The Exposed name column allows you to rename individual attributes in the payload independently of their domain model names.
Associations appear as a list of identifiers within the parent entity's event payload. Attributes and associations do not produce separate Kafka topics and show no Revision or Topic values of their own.
Revisions
Each tracked entity has a Revision number that identifies the schema of its event payload. Downstream consumers use the revision to detect and respond to schema changes. The major revision is also embedded in the Kafka topic name, so only breaking changes result in a new topic.
Studio Pro manages revisions automatically. When you modify the tracked configuration of an entity, Studio Pro marks it as Changed and calculates the new revision based on whether the change is breaking or non-breaking:
- Major revision (for example,
1.0→2.0) – a breaking change such as removing an attribute, renaming an entity's exposed name, or removing an entity from tracking. Consumers must be updated to use the new topic. - Minor revision (for example,
1.0→1.1) – a non-breaking change such as adding a new attribute. Existing consumers can continue reading the topic without modification.
Accepting Changes
Pending modifications are not finalized until you click Accept changes in the toolbar. Until you do, Studio Pro shows a consistency error on the document. You must resolve this error by accepting the changes before you can deploy the app.
Accepting changes confirms the new revision numbers and clears the modification states, leaving the document in a clean state ready for deployment.
Runtime Behavior
The following describe how the CDC service behaves at runtime:
- The CDC service runs in the system context, so no user security applies
- Events are published for every committed object change (create, update, and delete)
- Kafka topics are created automatically on deployment for each tracked entity
- Events use CloudEvents payload format, consistent with other Mendix Event Broker services